To understand where I'm coming from see my Fancast Avengers 3 part 1
http://www.comicbookmovie.com/fansites/ager/news/?a=62738
Which refers you to all of the preceding fancasts (also important) as well.
What we know:
Ross has now taken over SHIELD from Hill after the disappearance of Fury. Ross has depleted SHIELD and created, from it's ashes, HAMMER. He, as Iron Patriot leads his team of Thunderbolts, consisting of team leader, A-Bomb (Abomination), Titan, yet to be revealed as Nuke (Titanium Man), Winter Soldier, Namor, a reluctant Songbird and Constrictor, each representing a more "improved," militant version of the original group.
Iron Patriot (Hurt)
A-Bomb (Voiced by Roth) as opposed to Hulk
Titan (McCallan) as opposed to Iron Man
Winter Soldier (Stan) as opposed to Captain America
Namor (Witwer) as opposed to Thor
Songbird (Sackhoff) as opposed to Black Widow
Constrictor (Kinnaman) as opposed to Hawkeye
HAMMER, now in control of the Avengers and SHIELD, groups the super powered team, and SHIELD's top agents, with the Thunderbolts to stop Thanos.
All this in the absence of Hulk, who has been shuttled to a distant, uninhabited planet and Stark, who has been gravely injured.
Avengers consist of:
Cap (Evans)
Thor (Hemsworth)
Black Widow (Johansson)
Hawkeye (Renner)
Black Panther (Ejiofor)
Goliath (McGregor)
War Machine Cheadle)
Falcon (Fox)
Spider Woman (Blunt)
Tigra (Cole)
Wasp (Seyfried)
Vision (voiced by Bettany)
Mar Vehl (Strahovski)
Quicksilver (Peck)
Scarlet Witch (Lowndes)
13 (Sharon Carter) (Righetti)
That may seem like way too many but the focus revolves all around Ross, Thanos (more than anything) and the Twins. Every other member of Avengers has had moments to explore who they are.
Nova is still AWOL and Warlock is captured by Thanos.
Wanda and Pietro are classified as the deadliest Inhumans ever. Think Osama, Hitler, Stalin and all the rest rolled up into a pair.
They tend more towards the side of Ross' Thunderbolts over Avengers, whereas Songbird tends to the Avengers.
Although, the weird Wanda finds herself attracted to the synthazoid, Vision, none to happy is her hot headed brother
Throughout the movie, before the epic battle, Ross interrogates Stark multiple times for his knowledge. He tells the group that Stark is in a binge, he's staring at the reflection of his own demons at the bottom of a bottle.
Hulk is shown controlling himself from inside the small shuttle, gaining his composure and his hairline more and more. Gone is his beard and grey hair.
Explored, is Thanos' story.
His quest for the Gems and his loss to eventual keeper, Odin (a much younger version).
After Thunderbolts and Avengers beat the Wrecking Crew, staged, as we find out later, by Ross, in order to make heroes of his 'Bolts, Thanos brings the battle to Earth.
The Crew is attacked as to enact damage control. They seized control of the Flatiron Building, took hostages and demanded a ransom.
Hulk is shown crashing onto an unfamiliar planet.
"The Kree, the Chitauri and even the All-Father stood no chance. In all the realms, you are left, in my way,as a mere stepping stone to courting Death.
Chained to his side, like a beaten pet, is Warlock. Thanos reveals he has taken Warlock's soul.
My Beloved is bored with how easy this is for me. Gamora, my child, entertain the Mistress. Fight to the death, the Odinson and the Kree child.
Mar Vehl dies by a killing blow meant for Thor and Thor shouts "For Asgard!" before being killed himself in one final blow-to-blow.
The Mad Titan kills his daughter, ashamed it took her that long to win.
"My mate-to-be is still unaffected. I shall entertain a victory."
They give it everything they have and 1 by one he kills them all. Falcon and Goliath both are about to die and Wasp saves Falcon instead of Goliath. all 3 die regardless.
Widow and Hawkeye die together.
After Quicksilver is killed, Wanda unleashes some serious psych magic but is laughed at and killed just as fans get excited enough to get let down.
Don't think the Thunderbolts are staying alive, they die too.
All that is left Cap, Panther and Titan/Nuke. Panther dies, "Cap, you must stop him."
Thanos turns to his beloved and offers himself now that he has proven himself worthy and boasting of his achievement and his new-found status as Death's equal. Death congratulates his accomplishment, though still speaking through her various minions. When Thanos demands that Death address him personally as her mate, she points out to him, again through her minions, with his newly achieved status of omnipotence, Thanos is not her equal, but her superior, and that it would therefore not be fitting for her to address him directly. Thanos destroys the minion in a fit of anger, trying to comprehend his miscalculation, and finally wondering, while shedding a tear, how becoming God could prove such a hollow victory.
The weakness of Thanos wakens something within the souless Warlock and he fights Thanos with all of his might. When the 2 clash, Thanos, even with the gauntlet, can barely stand head to head with Him. Thanos shouts at Him, referring to Him as Magus.
When the 2 God-like beings clash it's immeasurable how devastating it is. Warlock can not outdo him.
Cap leaves his only surviving ally and staggers into the fight. Using Gamora's sword he cuts off the arm of Thanos, separating him from the Gauntlet. "Pathetic human. The All Father knelt before me. He, who was reborn from before, he, who sustains by consuming the essence of our universe, knelt before me. And you, a displaced, weak, mortal near death, defy me. Then you will choke on your bravado Earthling."
It's got to mean something, this scene has to set Cap apart from everyone.
Thanos, still powerful, even without the glove, kills Cap after about a minute, but remarks on the unprecedented struggle. "Gods are not that brave."
With Thanos distracted, Warlock obtains the Gauntlet, but in an instant, Nova appears, deeming Warlock unworthy of it, in part because of the threat of him eventually becoming the Magus.
During Warlock's temporary possession of the Gauntlet, he purges all good and evil from his being, leaving him entirely a creature of logic.
Nova reverses all that Thanos has done and turns Thanos into stone. Unfortunately, Cap was killed without the gauntlet and remains dead.
Death leaves, with the statue of Thanos held tightly, saddened her loss.
Nova gives Warlock the Soul Gem and takes the Space Gem himself. He tells the heroes and villains that the sorcerer supreme will helm the Reality Gem; the Power Gem will be given to King Blackagar; Time will be given to King Namor; Mind will be given to Stark.
Nova explains that he and Warlock must report to the Elders and will not return.
The end is Cap's funeral. Every Avenger save an imprisoned Hill and a missing Stark attend. Every Thunderbolt is there as well. It is televised and Ross does interviews in the background, soaking up the attention.
Bucky leans over the burial site and whispers "I remember, Steve."
Ross announces that, after these invasions, he has "been tasked to catalog all those who wish to use exemplary skills to combat good and evil. No longer will an action be taken on Earth without the government's knowledge and permission. Wide scale terrorism has been officially put in check."
"The Avengers have officially disbanded and any member of the team, or any within the sound of my voice, that wish to defend his or her country will do so under my leadership as a part of the Thunderbolts. I will not have another death on my hands due to one seeking fame by heroics. Every movement will be dictated by the government in order to sustain order."
"Welcome to the era of super human registration."
Mid-credits scene.
Songbird uncuffs Stark and they cautiously escape without being noticed.
Cast Additions:
Alex Pettyfer as Nova
I Am #4
Not a favorite of mine for much but it seems likely that, in the minimal scenes he has his fair popularity would do good to bring notability to the role. He's not that bad that he should be discredited and there's always the possibility, as with Black Panther, that, if the audience, responds well to his character, therein lies the potential for spin offs.
I will say that, of both the popular choices for Nova, Hedlund is a favorite of mine. I wanted a realistic approach to finding the right characters. Hedlund is bigger than what I've given Nova (minus possible spin offs) and would be more pricey for such a small role.

The Wrecking Crew...
Not enchanted by Norse magic, rather a group of criminals who got their hands on Pym Particles and mixed it something undiscovered to produce incredible genetic alterations in height, strength and invulnerability.
Wrecker
Joe Manganiello
True Blood
Joe is in dyer need of a comic book movie role and if it won't be Hercules or Superman than this is what I will settle for.
Pile Driver
Tyler Mane
X-Men
Bring him back as a subtle jab at the Fox franchise and use him wisely as the behemoth, Pile Driver.
Thunderball
Terry Crews
Expendables
With height alterations the man could scare a Thunder God.
Absorbing Man
Nathan Jones
I've seen this before and, although he's not my first choice, he works well in this land of giants.
Bulldozer
Conan Stevens
Stevens is one of the largest actors out there, and as Bulldozer, would crush all that don't believe in his ability.
Mr Hyde
Glenn Jacobs
See No Evil
Truly, an impressive, scary individual, Jacobs, a method actor, would be a very imposing Hyde.
Titania
Karen Cliche
Mutant X
A strong, beefy, and yet, attractive woman is what this role calls for. Cliche has that in spades.
NEXT: AVENGERS: CIVIL WAR